1. Field of the Invention
Aspects of the invention generally relate to an apparatus and method for heat processing substrates.
2. Background of the Related Art
In the fabrication of flat panel displays (FPD), thin film transistors (TFT) and liquid crystal cells, metal interconnects and other features are formed by depositing and removing multiple layers of conducting, semiconducting and dielectric materials from a glass substrate. The various features formed are integrated into a system that collectively is used to create, for example, active matrix display screens in which display states are electrically created in individual pixels on the FPD. Processing techniques used to create the FPD include plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), etching, and the like. Plasma processing is particularly well suited for the production of flat panel displays because of the relatively lower processing temperatures required to deposit film and good film quality which results from plasma processes.
During FPD processing, proper heat processing of the film across the entire surface of the substrate is critical for the FPD to function properly. The heating temperature required varies depending on the type of film being processed, and process being performed. For example, one exemplary type of flat panel display film used in the construction of FPDs is low temperature poly silicon (LTPS). Part of the LTPS film processing requires the LTPS film be heated up to about 600° C. to remove hydrogen from the film whereas a similar heat treatment for amorphous silicon α-Si) film requires a substantially lower temperature of up to 450° C.
Generally, the film heating process is highly temperature sensitive as temperature non-uniformity may cause insufficient removal of unwanted contaminates, resulting in peeling and ablation of the film. To compensate for temperature non-uniformity heating process times must be extended. Unfortunately, extending the heating process times increases the production cost and often results in unusable films if the process is not completed.
Conventional heating chambers provide heat processing by heating one or more substrates through a combination of gas conduction and heat radiation. Unfortunately, the chamber walls and other internal chamber components provide heat conduction paths within the chamber resulting in conductive heat losses. The conductive heat losses create a constantly fluctuating substrate-heating environment. As the temperatures are increased, conductive heat losses become more pronounced, exacerbating the heat non-uniformity within the substrate-heating environment. Moreover, conventional heating chambers are often very large to accommodate the substrate perimeter, further exacerbating the heating issues by increasing the area and volume to be heated. For example, as the demand for larger computer displays, monitors, flat-screen televisions, and the like increases a typical substrate may be 620 mm×750 mm, or larger. For instance, substrates of 1 meter×1 meter are contemplated. Typically, to compensate for the larger substrates, larger chamber volumes, and the subsequent increase in heat losses, more heating elements are used, thereby increasing the cost of the equipment, energy usage, and temperature non-uniformity. As temperatures increase, copper heating elements are often employed to offset energy costs and provide efficient heating. Copper heaters are generally more energy efficient than other types of heating elements. Unfortunately, as the temperatures are increased, copper atoms from the copper heaters often escape into the heating chamber and contaminate the film. Thus, traditional heating chambers and heating processes do not provide acceptably uniform and contaminant-free substrate heating for an efficient and cost effective substrate heating process.
Therefore, there is a need for a method and apparatus for uniformly heat processing a plurality of substrates in an efficient contaminate-free heat processing system.